The objectives of this project are to develop ligand binding radioassays which are specific for a given type or class of folate(s) coenzymes. The two primary classes are oxidized and reduced folates. Of the more physiologic reduced coenzymes, we wish to develop specific radiometric assays for methyltetrahydrofolate and formyltetrahydrofolate. The specific binding ligands for each folate will be obtained by extracting tissues, preparing membrane receptor sites or induction of antibodies by immunizing animals with coenzyme as a hapten coupled to a carrier protein. The coenzymes for each specific assay will be isotopically labeled by derivativization of the folate to a macromolecule which, in turn, will either be iodinated or chromated. As these specific radioassays are developed, they will be used to study the fraction of each folate in serum, red cells, and tissues as well as study the dynamics of absorption, transport and excretion. Finally, we are planning to develop a radioimmunoassay for a folate binding protein identified first in chronic myelogenous leukemia cells and serum but now believed to be in the cells and serum of other subjects. This radioassay will detect and measure this binder when saturated with endogenous folate. The method will be used to study this protein in folate deficiency, liver disease, and patients with malignancy.